The present invention relates to a run flat tire for motorcycles. More particularly, the present invention relates to a pneumatic run flat tire for motorcycles, which tire is provided with reinforced sidewall portions having such a high rigidity that, even when the tire is punctured during running, the tire can support the load of the motorcycle and maintain a high durability and a high stearing stability thereof when the motorcycle is either running straight ahead or making a turn.
In conventional pneumatic tires which are usually used for four-wheel and two-wheel vehicles, an air chamber formed inside the tire is inflated by compressed air and the load of the vehicle is supported by the inflated air chamber having a high elasticity. Therefore, the sidewall portions of the conventional tires have a relatively low rigidity. In this type of conventional tires, when the compressed air leaks from the air chamber and the pneumatic pressure of the air chamber becomes equal to atmospheric pressure, the tire will collapse at the portion thereof which is in contact with the road surface under the weight of the vehicle in such a manner that each of the sidewall portions of the tire is folded on itself so as to project outwards from the tire-mounting rim. In this condition, the collapsed tire cannot absorb the lateral force applied to the sidewall portions of the tire when the vehicle makes a turn. The lateral force applied to the tire when the vehicle makes a turn, includes a cornering centrifugal force which is produced by giving a slip angle to the tire relative to the longitudinal center line of the vehicle during turning and also includes a cambering centrifugal force which is produced by inclining the tire relative to the vertical direction in accordance with a camber angle. Therefore, the sterring stability of the vehicle is significantly reduced. Also, the collapse of the tire results in an irregular rotation of the tire. The irregular rotation causes the vehicle body to produce undesirable vibrations and thus remarkably reduces the handling stability of the vehicle. When the tire is subjected to such irregular rotation at a high speed for a long period of time, the tire is mechanically destroyed and also thermally decomposed to such an extend that the tire can no longer be repaired. Furthermore, the irregular rotation of the collapsed tire frequently produces a separation of the tire body from the tire-mounting rim and a lateral turning of the vehicle. Both of these conditions are very dangerous for a driver.
In order to eliminate the above-mentioned disadvantages of the conventional pneumatic tires, various attempts to obtain improvements of the pneumatic tires have been made. For example, in one attempt, the tire body was firmly fixed to the tire-mounting rim so that the tire cannot be removed from the rim even when the tire is punctured during running.
In another attempt, the tire was provided with a supporting member which extends from the rim into the air chamber so as to support the tread portion when the tire is punctured and thus collapses.
In still another attempt, the tire body was mounted on the rim in such a manner that the tire can be firmly combined with the rim. Accordingly, the rim can at its flange, support, the load applied to the vehicle during running.
In a further attempt, the sidewall portions of the tire were made of a highly rigid material so as to prevent the tire from collapsing when the tire is punctured.
In a still further attempt, in order to increase the rigidity of the sidewall portion, an elastic reinforcing member having a high stiffness was arranged in the tire. This reinforcing member extends from the head portion to the tread crown portion through the sidewall portion, and is effective for preventing the tire from collapsing when it is punctured.
The above-mentioned attempts are each effective for improving the steering stability, handling stability and durability of a tire for four-wheel vehicles when the tire is punctured, but not satisfactory for improving such characteristics of a tire for two-wheel vehicles, that is, motorcycles. In the case where the four-wheel vehicle is cornering, the tire can incline in a small angle. Therefore, the camber angle provided to the tire is in a narrow range. Accordingly, when the four-wheel vehicle makes a turn, the lateral force applied to the tire due to the cambering force is very small. That is, the lateral force consists essentially of only a cornering force. However, when the motorcycle makes a turn, it is necessary to incline the tire relative to the vertical direction by a large camber angle. This turn of the motorcycle in the inclined condition produces a large lateral cambering force together with the cornering force exerted on the tire. This great lateral force should be absorbed by the tire even when the tire is punctured for the safety of the driver. Accordingly, the above-mentioned attempts which are effective for improving the tire of the four-wheel vehicles, are not always satisfactory for improving the tire of motorcycles. Generally speaking, the run flat tire for motorcycles is required to have the following features.
1. The apparent configuration of the tire is similar to that of the conventional tires.
2. Even when the pneumatic pressure of the air chamber of the tire is reduced to atmospheric pressure, the tire can be partly deformed but not caused to completely collapse.
3. Even when the tire is punctured, the punctured tire does not cause the motorcycle to have a reduced steering stability and handling stability in either straight running or cornering.
4. Even if the tire is punctured while the motorcycle is running at a high speed of from about 150 to 200 km/hour, the irregular rotation of the punctured tire does not cause the motorcycle body to produce undesirable vibrations and the motorcycle can be stopped with a high handling stability after running over a certain distance.
5. Even after the tire is punctured, the motorcycle can still run for several hundred kilometers at a velocity of 100 km/hour or less.
6. The tire is provided with means for preventing separation of the tire from the tire-mounting rim when the tire is punctured.
7. When the tire is punctured, the tire can be completely repaired for reuse and such repaired tire will have a high velocity running durability similar to that of the non-punctured tire.
8. The tire is a tubeless tire having a high durability.
9. Since the motorcycle is supported by only two tires, the tires can stably support the motorcycle during straight running.
However, it has been found that no conventional tires for motorcycles could satisfy all of the above-mentioned features.
An object of the present invention is to provide a run flat tire for motorcycles, which has the same configuration and running features as those of the conventional run flat tire when the tire is inflated with compressed air, and which has a high steering stability even when the tire is punctured.
Another object of the present invention is to provide a run flat tire for motorcycles, which has such a feature that even when the tire is punctured during running at a high speed of, for example, from about 150 to about 200 km/hour, the body of the motorcycle does not produce any vibrations, the handling stability of the motorcycle, either in straight running or in cornering, is not reduced and the velocity of the motorcycle can be increased or decreased without difficulty.
A further object of the present invention is to provide a run flat tire for motorcycle, which has such a high durability that the tire can be run at a high speed, for example, of about 90 km/hour or more, over a distance of several hundred kilometers without thermal decomposition and mechanical destruction even after the tire is punctured and the pneumatic pressure inside of the tire becomes equal to atmospheric pressure.
The other object of the present invention is to provide a run flat tire for motorcycles, which is provided with reinforced sidewall portions having a proper rigidity and elasticity effective for preventing the tire from collapsing when it is punctured.